Blue-phosphorescent bis-cyclometalated iridium complexes with aryl isocyanide ancillary ligands

Abstract

The design of organometallic complexes with efficient blue phosphorescence remains a challenge in the field of optoelectronics. This paper describes a series of eight cationic, isocyanide-ligated bis-cyclometalated iridium complexes of the general formula [Ir(C^Y)2(CNAr)2](PF6), where C^Y is a triazole-based C^N cyclometalating ligand or an NHC-based C^C: cyclometalating ligand, and CNAr is an aryl isocyanide. The triazole- and NHC-derived cyclometalating ligands, in combination with the π-acidic isocyanide ancillary ligands, result in large HOMO–LUMO gaps and engender these compounds with photoluminescence in the blue region of the spectrum. The complexes are synthesized by a general synthetic procedure and isolated in moderate to good isolated yields, with a combination of NMR spectroscopy, mass spectrometry, and X-ray crystallography (for six of the eight compounds) establishing the identity and bulk purity of each compound. The redox properties of the compounds are studied by cyclic voltammetry, which provide evidence for the large HOMO–LUMO gaps that are critical for the blue photoluminescence. The triazole-based compounds are weakly luminescent in fluid solution at room temperature, and all complexes luminesce at 77 K in frozen solvent glass or at room temperature when immobilized in a transparent poly(methyl methacrylate) (PMMA) film. CIE coordinates for the photoluminescence spectra indicate pure blue emission for all compounds, with CIEy ≤ 0.15 for all but one compound.